1. Field of Invention
The present invention relates to a headphone assembly, and more particularly to headphones with distortion-free loudness limiting and dynamic equalization feature.
2. Description of Related Arts
In many applications of headphones, some automatic method of limiting the SPL (Sound Pressure Level) at the opening of the user's ear canals is highly desirable for the purposes of both comfort and hearing conservation. An automatic means is preferred over manual control because manual adjustment of listening volume tends to be less effective because as users listen to audio material, their hearing adapts to the sound level, causing some users increase the SPL as the listening session proceeds. Another reason manual control is less effective is because users sometimes cannot respond quickly enough to rapidly changing amplitudes of sound material to prevent hearing damage.
The prior art in automatic SPL limiting includes both active and passive circuitry to limit SPL. Active circuitry has the drawbacks of requiring a direct current power source and is often bulky.
Passive circuits known to date either simply reduce the efficiency of the headphones or clip the audio drive waveform, introducing severe distortion which makes their use unpleasing and also generates harmonics which results in low frequency power being shifted into higher frequencies where human hearing is more susceptible to damage, further reducing the effectiveness of simple clippers as automatic means of protecting hearing.